Biomedical imaging combines many principles of electrical engineering, physics, medicine, and biology. One emerging biomedical imaging modality is optical coherence tomography (OCT). OCT is the optical analogue to ultrasound imaging, except near-infrared light is used, rather than sound, to generate high-resolution, cross-sectional optical images based on the intrinsic optical scattering properties of tissue. Because light is used, cellular-level resolution, on the order of 5-10 microns, is feasible, to imaging depths up to 3 mm in highly-scattering tissue such as skin, or completely through the eye, the retina, and into the choroidal (vascular) areas behind the retina. There are numerous applications for OCT in medicine and surgery, where it can be thought of as performing an “optical biopsy” of tissue, rather than having to physically resect tissue, process it, and section it for observation on microscope slides using a standard white-light microscope.
OCT has been demonstrated extensively in medical, surgical, and biological applications since its inception in 1991, offering unique imaging performance including non-contact, high resolution, and real-time imaging. Among several applications, ophthalmic imaging using OCT has been the most successful application. First, the eye provides a uniquely suitable medium for OCT due to its transparent nature, minimal scattering, and excellent light penetration compared to other biological tissues. Second, imaging of the eye has grown significantly in importance for the diagnosis of ocular diseases. However, there are few techniques available other than scanning laser polarimetry and confocal scanning laser ophthalmoscopy.
Third, OCT provides information showing cross-sectional structures of the cornea and retina that cannot be obtained by any other non-invasive diagnostic technique, enabling an enhanced understanding of the pathogenesis of disease and the response to therapy. These properties have made OCT a unique ophthalmic diagnostic modality, and a commercially available product. The first commercially available OCT, called OCT 1000 (Carl Zeiss Meditec, Inc), was marketed in 1996. A variety of commercial ophthalmic OCT systems have since developed. In 2006, the first high-speed, high-resolution OCT 3 (Carl Zeiss Meditec, Inc) became the “gold standard” for retinal imaging. Current commercial ophthalmic OCT systems and their performance specifications are summarized in FIG. 1.